Method and apparatus for dewaxing oils



May 4, 1937 p. B. BANKS ET AL METHOD AND APPARATUS FOB DEWAXING OILS Filed April 13, 1934 Patented May 4, 1937 UNITED STATES PATENT OFFICE METHOD AND APPAJTUS FOR DEWAXING Application April 13, 1934, Serial No. '720,416

8 Claims.

The present invention relates to an apparatus for propane dewaxing and more specically to an apparatus for preventing vaporization oi propane from propane-oil solutions while'being pumped from one piece of equipment to another.

`In the operation of propane dewaxing plants considerable difliculty has been experienced in pumping oil-propane solutions due to the fact that it is impossible to insulate transfer lines and pumps thoroughly enough to preventabsorption of heat bythe oil-propane solution through such insulation. This absorption of heat is often sufilcient to raise the vapor pressure of the propane to a point above the capacity of thepump to pick up the solution, thus causing vaporization of propane and consequent vapor lock in the system. For instance, with propane at 30 F. a rise in temperature of-1 F. will cause a rise in pressure of about .5 pound per square inch and since the temperature of the outside air may be between 30 and 90 F., the temperature difference of 60-120 F. might easily cause a rise of several degrees Fahrenheit in the oil-propane solution, even with the best of insulation.

It is, therefore, an object of the present invention to provide an apparatus for the propane dewaxing of oil in which a rise in temperature o the solution being pumped is avoided.

The accompanying drawing illustrates diagrammatically one form of apparatus which may be used to practice the present invention.

In the drawing, I designates a storage tank for propane' or other light liquefied hydrocarbon refrigerant. Propane is withdrawn from the tank through valved line 2, having a valved branch 3 extending therefrom. Av pump 4 receives liquid flowing through the main line 2 and passes it under pressure to a rotary mixing device 5 through line 6. Meanwhile, wax-containing oil, which has been stored in tank 1 is withdrawn through valvedline 8 by means of pump 9 and is passed through line I0 to line-6, where it meets the propane from tank I and flows through the rotary'mixing device 5 and is intimately mixed therewith.

It is desirable that a heating coil I0 be supplied to oil storage tank 1 in order lto heat the oil sufficiently to impart enough heat so that the oilpropane mixture flowing from` the rotary mixing device 5 will have a temperature varying from 90 to 120 depending upon the viscosity and wax content of the oil to be'dewaxed.

'I'he oil-propane solution passes from the mixing device 5 through valved line I I to a. preliminary cooling coil I2 situated in propane chilling tank I3. Propane is admitted to the chilling tank I3 through line 3 by means of float controlled valve |30, the oat controlling the level of prochilled by permitting a portion of it to evaporate.

This is accomplished by opening valve I5 in line I4, leading to gaseous propane return header I6. Valve I5 may be thermostatically controlled, if desired, so as to maintain the propane within the tank I3 at an even predetermined temperature.

The propane-oil mixture inpassing through coil I2 Within the tank I3 is chilled to, say, 20 F. and passes from the coil through line I1 to the chiller and crystallizer I8. This chiller and crystallizer I8 is supplied with a vent line I9, equipped with a valve 20, to the gaseous propane return header I6. The oil-propane mixture within the chiller and crystallizer I8 is chilled to its final dewaxing temperature, which may be from -20 to 60 F., depending upon the degree of dewaxing desired, by'opening valve 20 in line I9 and permitting evaporation of propane from the propane-oil solution.

Chilling tank I3 is also used as for chilled propane to'be used in other parts of the system. Forv instance, sufficient propane may not be added to the o il in mixer 5 to give the complete degree of chilling required for dewaxing. It will therefore be necessary to add more propane, preferably chilledto the chiller and crystallizer I8. For this purpose the chilling tank I3 is provided with an outletA 2I having valved -branches 22 and 23. The valved branch'22 leads to a pump 24 having a jacket 25 around the pump cylinder. A valved line 26 leads from line 23 to this jacket and a vent line 21 leads from this chamber to the 4gaseous propane return header I6'. The outlet of the pump cylinder is connected to line 28 leading to valved line 29, which in turn leads to chiller and crystallizer `I8 and to' other apparatus, as will hereinafter be more fully described.

AThe chamber surrounding the cylinder of pump 24 is provided in order that liquid propane may be evaporated therein to chill the cylinder to a temperature below that of the propane being pumped and consequently prevent vaporization of the 'liquid propane being forced by the pump through line 28. Insulation has been found insuiiicient to prevent vaporization'of the propane, this vaporizatioircausingl a vapor lock, which in turn stops the flow of propane.

a storage tank Propane is withdrawn from the chilling tank I3 through lines 2l and 22 and is forced to the chiller and crystallizer I8 to supply additional propane which may be needed for finally chilling the propane-oil solution. The chilled propaneoil solution is passed, before the wax has settled, from thechiller and crystallizer I 8 through line 32 to pump 33 and is forced by'this pump through line 34 to and through a filter 30, which has a number of filtering units 3 I. Pump 33 is provided with a jacket 35 having a valved propane inlet 36 and a vent line 31 leading to gaseous propane return header I6. This pump jacket performs the same function as the jacket of pump 24, liquid propane being admitted through line 36 and vaporized within the jacket to cool the pump, the vaporized propane passing out through line 31.

Within the filter 30, the oil propane solution is separated from the crystallized wax by means of the filter units 3|. The oil-propane solution outows from the top of lter 3I through line 38 and valved line 39 to tower 40, wherein the propane still remaining in solution in the oil is vaporized. Tower 40 may be furnished with a steam coil 4I to provide any heat necessary to insure complete vaporization and separation of propane from the dewaxed oil. The dewaxed oil passes from the bottom of the tower through line 42 and the vaporized propane passes from the top of the tower through valved line 43 to the gaseous propane return header I6.

The wax separated by the filter units of the filter tank 3| is withdrawn through line 44 by means of pump 45. The wax separated from some oils does not separate readily from the filter elements and fall to the bottom of tank 30. It must therefore be removed. To accomplish this the ow of propane-oil solution to the filter is stopped and propane is passed from line 28 through line.

38 through the'ltering elements in the opposite direction to that taken by the oil-propane solution being filtered. The propane passing through the filter elements forces any accumulated wax from the filtering elements and washes it .out through the bottom of the tank through line 44. This wax propane slurry may then be separated by heating it in a tank, by means of a steam coil,

the tank having the proper gaseous propane vent. If desired, additional liquid propane may be added to the oil-propane solution passing into filter tank 3|] by means of the valved cross-connection 46 from line 28 to line 34.

The gaseous propane from return header I 5 is compressed by compressor 50 condensed in cooler 5I and returned to propane storage tank I through line 52.

From the foregoing it is apparent that the system described is capable of a smooth operation, free from the disadvantages caused by vapor lock troubles and clogged lters. Where, in the claims, propane is specified, it is meant to include all liquid normally gaseous refrigerants, such as sulphur dioxide, ethane propane mixtures, propane butane mixtures, butane, liquid carbon dioxide, or the like, when such refrigerant is being transferred under conditions of substantial vapor pressure equilibrium at a temperature substantially lower than the surrounding atmosphere.

Having noW described our invention, what we claim and desire to protect by Letters Patent is:

1. In a propane dewaxing system, a propane tank. an oil chilling and crystallizing tank, a pump for forcing propane vfrom the propane tank to the oil chilling tank, said pump comprising a pump chamber and a jacket closed from communication with the pump chamber, and means for admitting propane to and expanding propane within the pump jacket, thereby chilling the pump chamber and preventing evaporation of the propane being pumped therethrough.

2. In a propane dewaxing system, a propane tank, an oil chilling and crystallizing tank, a pump for forcing propane from the propane tank to the oil chilling tank, a second pump for removing the oil-wax-propane mixture from the chilling and crystallizing tank, each pump comprising a pump chamber and a jacket closed from communication with the pump chamber and means for admitting propane to and expanding propane within each pump jacket, thereby chilling each pump chamber and preventing evaporation of the propane flowing through each pump chamber.

3. In a propane dewaxing system, a propane storage tank, an oil storage tank, means for mixing oil and propane from said tanks, a propane chilling tank, a coil in said propane chilling tank for prechilling the oil-propane mixture, a chilling and crystallizing tank, means for feeding the prechilled oil-propane mixture to the chilling and crystallizing tank, means for adding propane to the prechilled oil-propane mixture in said chilling and crystallizing tank, said last means comprising a pump including a pump chamber and a jacket closed from communication with the pump chamber, and means for admitting propane to and expanding propane within the pump jacket under a pressure lower than that existing at the intake of the pump chamber.

4. In a propane dewaxing system, a propane storage tank, an oil storage tank, means for mixing oil and propane from said tanks, a propane chilling tank, a coil in said propane chilling tank for prechilling the oil-propane mixture, a chilling and crystallizing tank, means for feeding the prechilled oil-propane mixture to the chilling and crystallizing tank, means for adding propane to the prechilled oil-propane mixture in said chilling and crystallizing tank, a filter for the chilled propane-oil mixture, means for passing chilled propane-oil mixture from the chilling and crystallizing tank to the filter, said last means comprising a pump including a pump chamber and a jacket closed from communication with the pump chamber, and means for admitting propane to and expanding propane within the pump jacket under a pressure lower than that existing at the intake of the pump chamber.

' 5. In a propane dewaxing system, an oil chiller and crystallizer and means to supply propane thereto, a filter for the chilled propane mixture, means, including a pumpfor passing chilled propane-oil mixture from the chiller and crystallizer to the filter, said pump including a pump chamber and a jacket closed from communication with the pump chamber, and means for admitting propane to and expanding propane Within the pump jacket under a pressure lower than that existing at the intake of the pump chamber.

6. In a propane dewaxing system, a pre-Chiller adapted to receive propane and an oil-propane mixture in heat exchange relation, a chiller and v crystallizer adapted to receive the prechilled oilpropane mixture from the pre-Chiller, means, including a pump, for passing propane to the chiller and crystallizer, said pump including a pump chamber and a jacket closed from communication with the pump chamber, and means for admitting propane to and expanding propane within the pump jacket under a pressure lower than that existing at the intake of the pump chamber.

7. In 4the operation of dewaxing oil by means of a normally gaseous hydrocarbon wherein a liquid solution of oil and said hydrocarbon is pumped from one locus to another, the process of preventing absorption' of heat by the solution while being pumped with 'resultant danger of .vapor lock in the pump which comprises substantially surrounding the liquid solution while it is being pumped with said hydrocarbon in mainly'gas phase and under a pressure and temperature below the pressure and temperature of the vliquid solution being pumped. y

8. In the operation of dewaxing oil by means of a normally gaseous hydrocarbon wherein a. liquid solution of oil and said hydrocarbon is pumped from one locus to another, the process of preventing absorption of heat by the solution while being pumped with resultant danger of vapor lock in the pump which comprises flowing said hydrocarbon through a separate circuit in heat exchange relation but vout'ofcontact with the solution being pumped and reducing the pressure in said separate circuit to effect expansion of the hydrocarbon therein into a gas with resultant lowering of its temperature below that of the solution with which it is in heat exchange relation.

DANIEL B; BANKS. PAUL D. BARTON. 

